The water vapour self-continuum by CRDS at room temperature in the 1.6 µm transparency window
Résumé
The water vapour self-continuum has been investigated by high sensitivity Cavity Ring Down Spectroscopy at room temperature in the 1.6 µm window. The real time pressure dependence of the continuum was investigated during pressure cycles up to 12 Torr for fifteen selected wavenumber values. The continuum absorption coefficient measured between 5875 and 6450 cm-1 shows a minimum value around 6300 cm-1 and ranges between 1×10-9 and 8×10-9 cm-1 for 8 Torr of water vapour. The continuum level is observed to deviate significantly from the expected quadratic dependence versus the pressure. This deviation is interpreted as due to a significant contribution of water adsorbed on the super mirrors to the cavity loss rate. The pressure dependence is well reproduced by a second order polynomial. We interpret the linear and quadratic terms as the adsorbed water and vapour water contribution, respectively.